Castles featured walls as to seal off a hub to station units and supplies near strategic towns or structures, from where the defenders could easily reinforce the position. However, the dire need of regulating castle traffic became necessary and thus gates became chokepoints, which could be easily kept under garrisonal control. Needless to say, gatehouses often were very important weakpoints in a castle's design.
Gatehouses are massive in design, to withstand extensive enemy bombardment without crumbling. The gatehouse could also provide excellent height advantage to defenders atop, increasing combat efficiency. They soon became outfitted with additional features, such as drawbridges and arrow slits.